1. Field of the Invention
The present invention relates to an optical resonator in the fields of quantum information and optics.
2. Description of the Related Art
Upon implementation of a quantum computer using light or electromagnetic waves (to be simply referred to as light hereinafter), light needs to be associated with atoms, ions, quantum dots, and the like (to be simply referred to as particles hereinafter), which allow to preserve and manipulate quantum information, so as to preserve, manipulate, read, and so forth the quantum states of that computer. As one such method, a method of confining particles within an optical resonator, and coupling the resonance mode of the optical resonator and particles at a rate sufficiently higher (stronger) than a relaxation rate (decoherence rate: a rate at which normal quantum information is lost) of that system is available (for example, see JP-A 2001-209083 [KOKAI]). This resonance mode-particle coupling strength is observed as a Rabi oscillation. As one of important parameters that determine the Rabi oscillation, a mode volume of the optical resonator is known, and coupling becomes stronger with decreasing this value. However, in general, when the mode volume of the optical resonator becomes small, the photon lifetime (∝ Q-value) of the optical resonator is shortened, thus increasing the relaxation rate of that system. Therefore, it is desired to implement an optical resonator, the mode volume and photon lifetime of which are well-balanced.
Currently, as high-performance optical resonators which may be suited to quantum information processing, a photonic crystal optical resonator, microsphere optical resonator, toroidal optical resonator, Fabry-Perot optical resonator formed by a high-performance DBR, and the like have been proposed (for example, see JP-A 2001-209083 [KOKAI], and Physical Review A, 2005, [vol. 71] 013817-1-10).
Upon implementation of a quantum computer, as an amount that gives an indication of limitations on its feasibility and performance, a ratio between a decoherence time (relaxation time) and arithmetic time (or quantum gate operation time), i.e., how many times a quantum gate operation can be performed until a system decoheres, gives an important indication. On the other hand, as a method of implementing a quantum computer, a method of using light or electromagnetic waves (to be simply referred to as light hereinafter) and using a coupling system of the resonance mode of an optical resonator and particles is known. Letting κ be the attenuation rate of the optical resonator, γ be the relaxation rate of particles, and g be the strength of resonance mode-particle coupling, since the quantum gate operation time is limited by g, satisfying g>κ+γ serves as one guideline. Note that g is determined by the physicality unique to particles and the mode volume of the optical resonator. κ is an inverse number of the photon lifetime of the resonance mode, which is determined by absorption, scattering, leakage, and the like of light in the optical resonator, and is in inverse proportion to a Q-value. γ is the rate of relaxation of the quantum state in particles, and is determined by the physical systems and environment (crystal field, magnetic field, temperature, etc.) of particles.
Of the currently proposed optical resonators, a photonic crystal resonator has a small mode volume, but it is hard to say that its photon lifetime is sufficiently long, and available physical systems are limited. Conversely, a Fabry-Perot resonator can generally easily increase the photon lifetime. However, in this case, the mode volume of the Fabry-Perot resonator becomes larger than other resonators, and g is insufficient with respect to γ. As a microsphere resonator and toroidal resonator, those having high resonator performance can be obtained even in status quo, but further improvement of performance is demanded. Therefore, implementation of an optical resonator having a good relationship among g, κ, and γ is demanded.